This invention relates to thermal ink jet printing, and more particularly, to an improved method of fabricating a thermal ink jet printhead by use of a filler material in the internal cavities of bonded ink jet silicon wafers which is solid or gels at room temperature during the dicing operation which separates the bonded wafers into a plurality of individual printheads.
Thermal ink jet printing is a type of drop-on-demand ink jet systems, wherein an ink jet printhead expels ink droplets on demand by the selective application of a current pulse to a thermal energy generator, usually a resistor, located in capillary-filled, parallel ink channels a predetermined distance upstream from the channel nozzles or orifices. The channel end opposite the nozzles are in communication with a small ink reservoir to which a larger external ink supply is connected.
U.S. Pat. No. Re. 32,572 to Hawkins et al discloses a thermal ink jet printhead and several fabricating processes therefor. Each printhead is composed of two parts aligned and bonded together. One part is a substantially flat substrate which contains on the surface thereof a linear array of heating elements and addressing electrodes, and the second part is a substrate having at least one recess anisotropically etched therein to serve as an ink supply manifold when the two parts are bonded together. A linear array of parallel grooves are also formed in the second part, so that one end of the grooves communicate with the manifold recess and the other ends are open for use as ink droplet expelling nozzles. Many printheads can be made simultaneously by producing a plurality of sets of heating element arrays with their addressing electrodes on a silicon wafer and by placing alignment marks thereon at predetermined locations. A corresponding plurality of sets of channel grooves and associated manifolds are produced in a second silicon wafer. In one embodiment, alignment openings are etched in the second silicon wafer at predetermined locations. The two wafers are aligned via the alignment openings and alignment marks, then bonded together and diced into many separate printheads.
U.S. Pat. No. 4,638,337 to Torpey et al discloses an improved thermal ink jet printhead similar to that of Hawkins et al, but has each of its heating elements located in a recess. The recess walls containing the heating elements prevent the lateral movement of the bubbles through the nozzle and therefore the sudden release of vaporized ink to the atmosphere, known as blow-out, which causes ingestion of air and interrupts the printhead operation whenever this event occurs. In this patent a thick film organic structure such as Riston.RTM. or Vacrel.RTM. is interposed between the heater plate and the channel plate. The purpose of this layer is to have recesses formed therein directly above the heating elements to contain the bubble which is formed over the heating elements, thus enabling an increase in the droplet velocity without the occurrence of vapor blow-out and concomitant air ingestion.
U.S. Pat. No. 4,878,992 to Campanelli discloses an ink jet printhead fabrication process wherein a plurality of printheads are produced from two mated substrates by two dicing operations. One dicing operation produces the nozzle face for each of a plurality of printheads and optionally produces the nozzles. This dicing blade, together with specific operating parameters, prevent the nozzles from chipping and the nozzle faces from scratches and abrasions. A second dicing operation with a standard dicing blade severs the mated substrates into separate printheads. The dicing operation which produces the nozzle face is preferably conducted in a two-step operation. A first cut makes the nozzle face, but does not sever the two mated substrates. A second dicing cut severs the two substrates, but does so in a manner that prevents contact by the dicing blade with the nozzle face.
In all ink jet printing systems, the nozzle or orifice size, shape, and surface conditions affect the characteristics and trajectory of the ink droplet emitted from the nozzle. Some ink jet printers have a separate nozzle plate which is independently fabricated to obtain the desired dimensional tolerances and surface conditions. This nozzle plate is then aligned and bonded to the droplet generator or printhead. In addition to the dimensional precision, attachment is sometimes difficult and debonding is a constant concern. Also, if an adhesive is used, it may flow into the nozzle or ink paths, thereby restricting or impairing the droplet ejection and/or trajectory. Other ink jet printers have printheads fabricated from two substrates, as disclosed in the prior art discussed above, in which one substrate contains the heating elements and the other contains ink recesses, which, when the substrates are aligned and bonded together, serve as ink passageways. The open ends of the passageways terminate about 1.0 to 5.0 mils in front of the heating elements and create the nozzles. The front face of the printhead containing the nozzles have a major impact on the droplet characteristics and trajectories. One discontinuity at the nozzle is made by chipping of the unsupported edges of the channels during the dicing operation which concurrently forms the nozzle face and nozzles by cutting across one end of the channels in a direction perpendicular thereto. A second problem with severing bonded silicon wafer pairs in a plurality of individual printheads, is that dicing debris is readily forced through the nozzles and wedged into the channels. The dicing debris is usually difficult, if not impossible, to remove because of the relatively small cross-sectional areas of the channels and nozzles.
This invention overcomes the above-mentioned two problems associated with the standard dicing techniques used to separate bonded, thermal-ink-jet, silicon-wafer pairs into a plurality of printheads.